Many engines have already been designed to that end. There are thus well-known spark-ignition four-stroke engines with four valves per cylinder, a spark plug situated in the cylinder head on the longitudinal axis of the cylinder, with the cylinder having intake pipes positioned running substantially parallel to the axis of the cylinder, and into which the fuel-injection nozzle opens just below the intake valves.
Also known are engines of the same type but where the intake pipes are positioned so as to produce a motion of the gases around the axis of the cylinder (a motion referred to as swirl).
The piston associated with these engines commonly has a specifically shaped hollow intended to direct and to intensify the motion of the gases in the combustion chamber.
There are also well-known engines whose piston has a spherical bowl (or hollow) situated at the top dead center, just opposite the fuel-injection nozzle and the spark plug.
All these engines have large capacities (cylinder bores rather above 80 mm) and they all have at least four valves per cylinder.
They allow combustion in a stratified mode at low loads and/or so-called homogeneous combustion at high loads.
The combustion is referred to as stratified when a zone of the combustion chamber contains a richer mixture than the rest of the chamber, at low loads. This allows easier ignition of the mixture since the enriched zone is globally close to the spark plug.
At high loads, so-called homogeneous combustion is recommended. The mixture then has to be very homogeneous in the whole of the combustion chamber.
Direct injection engines currently work properly either in one mode or in the other. It is generally difficult to reconcile both operating modes.
In such engines, the size, the accessibility and the cost are important parameters.